Synchro devices, such as synchro resolvers, are widely utilized in the indication of measurement of the angular position of a shaft or other rotatable member. Normally, the rotor winding of a synhcro resolver is excited by a sinusoidal voltage. This voltage couples to a set of output windings which provide separate output voltages proportional to the sine and cosine of the angle at which the rotor is positioned. Conventionally, these output voltages are converted to D.C. signals proportional to the respective sine and cosine values and are of a polarity in accordance with whether the output voltage is in phase or out of phase with the exitation voltage. Further, conventionally, bulky and expensive synchronous demodulators are employed to make this conversion to D.C. As a means of overcoming these disadvantages, it has been previously proposed, e.g, in U.S. Pat. Nos. 4,270,077 and 4,334,179, that one may do away with synchronous demodulators by exciting the rotor winding of a synchro resolver with a pulse and computing shaft angle from the amplitude of the resulting pulse shaped voltages induced into the stationary windings. As is commonplace in data systems handling any different signals, with respect to which sine and cosine signal values are only two, signals are fed through an analog multiplexer and then processed on a serial basis by a central signal processor or computer. This means that sampled voltages are obtained at different times. Insofar as the two sine and cosine signals we are dealing with, it means that they do not necessarily reflect the same shaft position and thus some error is introduced in the computation of a shaft angle. While perhaps in many applications the error is not significant, there are still many applications where precision of resolution, for example, on the order of 1 to 2 minutes of arc, are essential. Applicants find that in order to reliably accomplish this, improved circuitry is required.
Accordingly, it is the object of this invention to provide a synchro resolver type angular measurement system with enhanced accuracy and in addition one which is readily adaptable to employment with a variety of synchro reslvers which, for example, may be adapted to normally operate at a variety of frequencies, for example, 60 cycle or 400 cycle, with minimal circuit adjustment.